The present invention relates to a valve for regulating fluids with a piezo-electric actor unit for operating a valve member assembly.
DE 199 46 833 A1 discloses a valve for regulating liquids with a piezo-electric actor unit for operating a valve member, which is axially displaceable in a bore of a valve body and on one end, has a valve-closing member, which cooperates with at least one seat on the valve body for opening and closing the valve. In this manner, the valve-closing member divides a low-pressure region from a high-pressure region, which, for example, represents a rail pressure region in a common rail injection valve of a motor vehicle. The valve member is separately formed with first and second pistons, which are separated from one another by means of a hydraulic chamber operating as a hydraulic converter.
With the type of valves in which the stroke or lift of the actor is increased with a hydraulic coupler, the action of the force on the volume of the hydraulic chamber, for example, via the column delimiting the pistons, causes leakage loss, which leads to an inaccuracy on subsequent valve operations, in the event no refilling of the hydraulic chamber takes place.
For the refilling of the hydraulic chamber, it is proposed in DE 199 46 833 A1 to provide a refilling device for removal of the hydraulic fluid of the high-pressure region, which is formed with a channel having a throttle bore. For refilling of the hydraulic chamber, the channel opens into a column surrounding the first and/or second piston and which has a branch to a valve low-pressure chamber via an overpressure valve. The valve low-pressure chamber is bordered by a valve seat that is displaceable by the valve-closing member. This type of valve construction with this type of refilling device, however, is relatively expensive.
Based on reasons of cost and function, in subsequent developments, the entire valve region from the hydraulic chamber to the valve seat of the valve closing member was formed as a system pressure region, whereby the refilling step takes place simultaneously with the opening of the valve closing member.
With this type of solution, which will be described in greater detail below with reference to FIG. 1, the constructive change of the refilling of the second piston is biased through a spring with minimal tensioning, whereby the necessary pressure difference for supplying is formed and the second piston remains in position on the valve closing member.
However, as previously noted, a spring is necessary for biasing the piezo-electric actor unit and a further spring of the valve must be hereby coordinated. This can create problems due to minimal space, since a similar and easily reacting spring requires a correspondingly large length.
In this regard, the realization of an exactly measured, multiple injection difficult, since the spring-loaded second piston can swing through powerfully upon multiple injections under certain circumstances, whereby a correspondingly large quantitative tolerance is provided.
The valve of the present invention, in which the second piston is supported on the valve body in the direction of the hydraulic chamber via at least an approximately casing-type spacer surrounding the hydraulic chamber, represents an optimization of the hydraulic coupler function of the hydraulic chamber relative to refilling.
If one were to compare the refilling of the hydraulic chamber by using a spacer as opposed to a spring, a quicker refilling of the hydraulic chamber takes place, since the refilling no longer takes place corresponding to the ratio of the spring force on the second piston with reference to the cross sectional surface of the second piston, rather takes place directly with the surrounding system pressure.
Upon many quick, successive operations of the valve, which occur in multiple injections of the valve in an fuel injection valve, as noted above, it is advantageous with the embodiment of the present invention with a spacer for supporting the second piston on the valve body that the spacer represents a type of an overstroke stop and prevents a swinging-through of the second piston. By the use of this type of fixed stop of the second piston against the hydraulic chamber, for example, the quantitative tolerances that occurred with multiple injections can be specifically reduced.